A Novel Vortex Generator for Mitigation of Shock-Induced Separation

Abstract

A new geometry of a sub-boundary-layer vortex generator, which is termed as a slottedramp vortex generator, is proposed here. The geometry of the vortex generator is that of a ramp (triangular wedge) which has a semi-circular groove at its base. The centerplane of the groove or slot, which is basically like a tunnel that runs across the length of the ramp, is located at the spanwise plane of symmetry of the ramp. Preliminary computations of supersonic flow at a free-stream Mach number of 2.5 are conducted over vortex generators 2 mm, 3 mm, and 4 mm high. For each device height h, the flow is simulated for three values of the slot radius -0.2h 0.3h, and 0.4h. The incoming flow profile is based on the experiments conducted by Dr. Babinsky at Cambridge on control of shock/boundarylayer interaction with micro vortex generators at a free-stream Mach number of 2.5. An immersed-boundary technique suitable for high-speed turbulent flows is used for rendering the vortex generators. Comparisons are presented between the different slotted-ramp vortex generators with a standard ramp based vortex generator of the same device height using streamwise velocity profiles at different locations downstream of the device. Velocity plots show that the new device results in higher streamwise velocity along the centerline in the near wake region for the larger sized vortex generators and the effect improves when a higher slot radius is used. Comparisons are also presented with the standard ramp type vortex generator using span-averaged total pressure profiles and momentum-deficit contours at different streamwise locations, and near surface axial velocity contours. Finally, results from computations of an impinging oblique-shock/boundary-layer interaction for a flow turning angle of 7 degrees at Mach 2.5 with and without flow control are presented. To achieve flow control two different cases are considered -one using an array of 3 x 3 mm high slotted-ramp vortex generators and the other using a similar array of the ramp type vortex generator. All the computations done as part of this study solves the Reynoldsaveraged Navier-Stokes equations with Menter's k − ω/k − turbulence model (baseline or SST formulation).Nomenclature h height of vortex generator r slot-radius of vortex generator x streamwise distance measured from the inflow plane of computational domain X streamwise distance measured from the trailing edge of vortex generator y, Y vertical distance measured from lower wall of computational domain Z spanwise distance measured from centerplane of computational domain

Flow Control in a Mach 4.0 Inlet by Slotted Wedge-shaped Vortex Generators

“…This immersed-boundary method is suitable for high-speed turbulent flows and has been used previously with success to simulate flows with similar flow-control devices. 9,10,13,17 The L 2 norm of the residual and the net mass balance are monitored for checking the convergence of the solution. The solution is considered converged when the normalized residual -with respect to the starting residual -reaches a value of about 1.0E − 08.…”

“…Since a sub-boundary layer device is considered for this study, a device height h of 2 mm is selected with a slot with r/h of 0.6 where r is the radius of the slot. 13 This ensures that for all the streamwise locations considered for positioning the VG, the height of the device is less than 50% of the incoming boundary layer thickness. The effect of the side wall is neglected in this study and the device is placed such that the spanwise central plane (which is also the plane of symmetry) of the vortex generator is at a distance of z/h =3.75 from the symmetric boundary of the domain(at z = 0).…”

“…This device has been shown to perform better than a conventional/standard vortex generator in reducing flow separation. 13 An isometric view of the slotted vortex-generator is shown in fig 1. The work comprises of two main parts: the first part includes a set of simulations with inviscid inlet sidewalls and attempts to determine an optimum streamwise positioning of the device; the second part takes into account the presence of the inlet sidewall -treating the same as no-slip wall -in the attempt to provide some direction about the effect of the device in the presence of side-walls.…”

“…This includes use of devices like vortex generators (wedges, vanes, and doublets) 5, 7-9, 11 , aero-elastically deflecting flaps [2][3][4]10 , and jets 6 of fluids among other devices. A majority of the numerical simulations/experiments performed to investigate and design such devices have used idealized computational domains with periodic boundary conditions in the spanwise direction 2,7,8,11,13 / ignored effects of wind-tunnel sidewalls [3][4][5] in wind-tunnel test sections. As such, these studies have typically ignored the effects of the sidewall -which is present in an actual inletin determining the design of SBLI control device.…”